The present study was to trace the neuronal pathway in the spinal cord and brainstem following noxious stimulation and acupuncture plus noxious stimulation by using immunohistochemical technique to detect the expression of c-fos like protein. The results showed that in both the noxious stimulation group and acupuncture of Zusanli(St.36) and Lanwei(Extra 33) points plus noxious stimulation group a lot of Fos-like immunoreactive (FLI) cell nuclei appeared in the following structures: dorsal horn of lumbar and sacral spinal cord (Laminae I, II, V and X), n. reticularis lateralis, n. reticularis paragigantocellularis lateralis, area A1, n. tractus solitarii, n. raphe magnus, locus coeruleus, n. raphe dorsalis and the periaqueductal grey. In the control group no obvious c-fos expression was shown in the structures mentioned above. It was also shown that in the lumbar and sacral spinal cord the number of FLI nuclei in the acupuncture plus noxious stimulation group was more than that in the noxious stimulation group, but in locus coeruleus and the ventral part of the periaqueductal grey the number of FLI nuclei in the acupuncture plus noxious stimulation group was less than that of the noxious stimulation group. The results imply that acupuncture and noxious stimulation may activate the intrinsic pain modulating system through the spinal dorsal horn, then suppress the c-fos expression induced by noxious stimulation in the locus coeruleus and ventral part of the periaqueductal grey.